The invention relates to a drive assembly of a motor vehicle having an internal combustion engine.
It is known to drive motor vehicles via internal combustion engines (hereinafter simply engines). These engines must be rotated up to speed for starting, until the engine begins to run on its own as a consequence of incipient combustion moments. To crank the engine, i.e., to turn it over, it is known to run the engine up to speed with an electric starter, whose pinion meshes with a toothed ring disposed on an engine crankshaft in a manner fixed against relative rotation and starts to turn it. This cranking device has stood the test of time but has the disadvantage of being noisy; also, because of parts subject to mechanical wear, the engine can be started with it only a limited number of times.
By realizing novel vehicle concepts which seek in particular to reduce fuel consumption, engines must be subjected to a high number of starting cycles. To save fuel, engines are turned off when the vehicle is stopped, for instance at a traffic light, in the so-called start-stop engine operating mode, and then automatically cranked again and started when the vehicle is to be driven onward again.
It is known to use electrical machines that are operated in the motor mode and the generator mode and are connected in force-locking fashion to a crankshaft of the engine. In the motor mode, direct starting of the engine can be done; after the engine runs up to speed, the electrical machine is switched over to a generator mode and serves to furnish a supply voltage for the motor vehicle. A disadvantage here is that particularly in cold starting, the electrical machine must be excessively oversized if it is to bring the requisite starting power to bear.
A so-called internal direct start is also known, in which the crankshaft, via a positioning device, is brought into a defined position so that the piston of a starting cylinder--a particular defined piston from among the total number of pistons of the engine--is brought into a starting position, stays there, and then by injection and ignition of fuel, a first combustion moment is generated, which is utilized to crank the engine. A disadvantage here is that because of the prepositioning time, only relatively poor starting dynamics are attainable, so that the engine does not begin to run on its own until after a relatively long time.